1. Field
One embodiment of the invention relates to a video reproduction apparatus, a video reproduction method, and a video reproduction process program which are used to reproduce digital video signals subjected to a efficient compression coding process using an inter-frame prediction coding technique, from an information recording medium, and in particular, to improvements in a video reproduction apparatus, a video reproduction method, and a video reproduction process program which perform forward and reverse variable-speed reproductions.
2. Description of the Related Art
As is well-known, efforts have been made to reduce the amount of information in video signals to be digitally recorded on an information recording medium, for example, a hard disk, by subjecting the video signals to an efficient compression coding process. As an efficient compression coding process of this kind, the Moving Picture Experts Group (MPEG) scheme is currently commonly adopted.
The MPEG scheme specifies three types of video frames: intra (I) frames, predictive (P) frames, and bidirectionally predictive (B) frames. Of the three types of frames, the I frames correspond to intra-frame coded videos coded using only intra-frame information. Video signals for one frame can be restored using only the I frames.
The P frames correspond to inter-frame forward prediction coded videos predicted on the basis of past frames. The P frames may involve inter-frame reverse prediction coding that predicts videos on the basis of future frames. The B frames correspond to inter-frame bidirectional prediction coded videos predicted on the basis of both past and future frames.
The MPEG scheme records and reproduces video signals on and from the information recording medium in group-of-picture (GOP) units; a GOP contains the three types of frames having respective predetermined numbers of frames. This enables random accesses to allow performance of various special reproduction operations such as reproduction from any position, forward and reverse variable-speed reproductions, and still reproduction.
Among the special reproduction operations, the forward and reverse variable-speed reproductions are generally achieved by searching for the I frames present in GOP read from the information recording medium, subjecting the I frames to a decoding process, and displaying the decoded video frames forward or in reverse along a time sequence.
However, one GOP is ordinarily often composed of 15 frames, one I frame, four P frames, and 10 B frames and thus contains an amount of information corresponding to a video display time of about 0.5 seconds. Thus, the simple technique of decoding and displaying only the I frames in each GOP fails to display videos with smooth motions particularly during the reverse variable-speed reproduction.
Jpn. Pat. Appln. KOKAI Publication No. 2003-244641 discloses a technique of enabling smooth reverse reproduction by, during forward data reproduction, storing stream data obtained by decoding coded data, in a buffer area, and during reverse data reproduction, reading the decoded stream data stored in the buffer area for display.